Apparatus and method applying vibratory energy



c. A. BOYD 3,209,574

APPARATUS AND METHOD APPLYING VIBRATORY ENERGY Oct. 5, 1965 Filed NOV.4, 1963 QR FII 1 I i I 1 IL Q 3% Q Q% Nw v Qw h mw Rw E- Q w 4 3% kw 4Q? Q d -$v QM d Q \& mu Rn M D ww wa M W S A United States Patent3,209,574 APPARATUS AND METHOD APPLYING VIBRATORY ENERGY Charles A.Boyd, West Chester, Pa., assignor to Aeroprojects Incorporated, WestChester, Pa., a corporation of Pennsylvania Filed Nov. 4, 1963, Ser. No.321,041 '10 Claims. (Cl. 72-283) The present invention relates to amethod and apparatus applying vibratory energy, and more particularly toa method and apparatus for applying vibratory energy in floating plugdrawing of articles including tubing.

The apparatus and methods by which tubing may be drawn can be classifiedunder several headings:

(1) Sinking.This is the drawing of tubing through an appropriate diewhich results in a decrease in the outside diameter of the tubing. Sinceno constricting force is applied to the inside surface of the tubing,the wall thickness of the tubing does not change much.

(2) Mandrel drawing-This is the drawing of tubing through an appropriatedie which results in a decrease in the outside diameter of the tubing.However, the tubing is also drawn over a mandrel having an outsidediameter equal to the final inside diameter desired for the drawntubing. The mandrel moves with the drawn tubing and is removed in asubsequent step of the operation. Mandrel drawing results in a decreaseof both outside diameter and wall thickness of the tubing.

(3) Plug drawing.-This is the drawing of tubing through an appropriatedie with a plug on the inside of the tubing which fixes the innerdiameter of the drawn tubing. This plug is maintained at a fixedposition relative to the die in two general ways: (a) back supportedplug. The plug is held in position by a supporting rod which is threadedthrough the undrawn portion of the tubing and fastened to a rigid memberof the draw bench; (b) floating plug. The plug is of such configurationthat at the appropriate position relative to the die, the frictionalforce tending to draw the plug deeper into the die is counterbalanced bythe force of deformation of the tubing. This results in the plugs beingmaintained in an equilibrium position.

It can be seen that the floating plug drawing and the sinking processcan be used on long lengths or coils of tubing, whereas the othermethods can be used only on discrete straight lengths.

It has been proposed heretofore to employ vibratory energy when drawingmaterial, as in United States Patents 2,393,131; 2,568,303; and2,638,207 which are not known to have been commercialized, apparentlybecause of significant deficiencies with respect to the application andutilization of the vibratory energy there described.

Various improvements in employing vibratory energy when drawing materialhave been proposed, as in United States patent application Serial No.289,559 entitled Vibratory Energy Method and Apparatus, filed June 21,1963, in the names of Charles A. Boyd et al.; United States patentapplication Serial No. 289,694 entitled Method and Apparatus EmployingVibratory Energy, filed June 21, 1963, in the names of Charles A. Boydet al.; United States patent application Serial. No. 289,558 entitledMethod and Apparatus Utilizing Vibratory Energy, filed June 21, 1963, inthe name of Charles A. Boyd et a1. and United States patent applicationSerial No. 303,022 entitled Method and Apparatus Using Vibratory Energy,filed August 19, 1963 in the name of Charles A. Boyd et a1. However,neither the method nor the apparatus of the present invention has beendescribed therein.

Accordingly, it is an object of this invention to provide an improvedmethod and apparatus for drawing of tubing.

Another object of the invention is to provide an improved floating plugsystem for drawing of tubing under vibratory energy application.

It is also an object of this invention to provide an improved fioatingplug system for drawing of tubing under vibratory energy applicationwithout the necessity for joining the plug securely to a source ofvibratory energy.

A further object of this invention is to provide an improved method andapparatus for continuous drawing of tubing.

These and other objects of the invention are accomplished by providing aplug having a controlled acoustical geometry and by drawing with saidplug under the influence of a vibratorily activated die.

For the purpose of illustrating the invention, there is shown in thedrawings forms which are presently preferred, it being understood,however, that this invention is not limited to the precise arrangementsand instrumentalities shown.

FIGURE 1 is an elevational view of apparatus embodying the presentinvention, partly in section and partly in diagrammatic form.

FIGURE 1A is an enlarged sectional view of a fragment of the apparatusillustrated in FIGURE 1.

Referring to the drawings in detail, wherein like numera-ls indicatelike elements, there is shown in FIGURE 1 a vibratory tube drawingapparatus designated generally as 10.

The apparatus 10 is in the nature of a draw bench and includes a die 12having an orifice 14. A floating plug 16 (see FIGURE 1A) extends into orthrough the orifice 14 and defines with the die 12 a restrictedpassageway through which the tube material 30 is drawn.

Die 12 is an element of a transducer-coupling system (designatedgenerally as 38), other elements of which are acoustical coupler 40(which includes [a plurality of horns 44a, 44b, 44cand 44d not shown)and a plurality of transducers designated 50a, 50b, 50c, and 50d (thelast not shown).

System 38 is designed to operate at a given frequency, which ispreferably. a resonant frequency. System 38 is preferably dimensioned tohave an over-all physical length equivalent to an acoustical length of awhole even number multiple of a one-half wavelength in the material ofwhich it is made at the said frequency, so as to have, for efficientoperation, an antinode (loop) area of the vibration at thetube-contacting portion of the die.

Each of the transducers 50a, 50b, 50c, and 50d may be of themagnetostrictive type as shown and of conventional constructioncomprising a half-wavelength-long laminated core of nickel, nickel-ironalloy, or other magnetostrictive material, properly dimensioned toinsure axial resonance with the frequency of alternating current appliedthereto by coil 68 so as to cause it to increase or decrease in lengthaccording to its coeflicient of magnetostriction. The detailedconstruction of a suitable magnetostrictive transducer is well known tothose skilled in the art and does not form a part of the presentinvention and, accordingly, no description of its construction will bemade herein. It will be appreciated by those skilled in the art that inplace of the magnetostrictive transducers 50a, 50b, 50c, and 50d, otherknown types of transducers may be substituted; for example,electrostrictive or piezoelectric transducers made of barium titanate,quartz crystals, lead zirconate titanate, etc., may be utilized.

Each of transducers, 50a, 50b and 500, and 50d is provided with anexcitation coil 68 and a polarizing coil 70. Excitation coils 68 oftransducers 50a, 50b, 50c and 50d are connected to a power supply(incorporating an ampliher, not shown, and oscillator, not shown)suitable for powering the transducers 50a, 50b, 50c, and 50d; suchequipment well known to the art. The desirability of magneticallypolarizing the magnetostrictive transducers 50a, 50b, 50c, and 50d bymeans of polarizing coils 70, in order for the metal laminations in saidtransducers to elficiently convert the applied energy from excitationcoils 68 into elastic vibratory energy, is also readily understood bythose skilled in the art. Low voltage direct current can be supplied tocoils 70 by battery, rectifier, or other means well known to the art.

The aforesaid power supply system, in a typical example, is capable ofproducing electrical signals in the range of between about 60 cycles persecond and about 300,000 cycles per second. This frequency range issuitable for purposes of the present invention, including as it doesfrequencies in both the audible range (such as up to about 15,000 cyclesper second) and the ultrasonic range (generally above about 15,000cycles per second). A preferred frequency would be in the range of fromabout 3,000 to about 50,000 cycles per second with the optimum beingbetween about 14,000 to about 35,000 cycles per second. Normally, afrequency is chosen which will provide a suitable size of apparatus fora given application or set of applications, with the ultrasonic rangehaving the further advantage of inaudibility for op erator comfort.

Thus, transducer-coupling system 38 may be constructed to operate at15,000 cycles per second, for example.

As is well known to the art, the electrical frequency of the alternatingcurrent power supply (such as 60 cycles per second) is changed to matchthe mechanical or elastic vibratory frequency of the transducers (15,000cycles per second in this example, as aforesaid).

It is to be noted that the source of high frequency alternating currentmay be a motor alternator having suitable frequency control, and thatsuch a motor alternator source is particularly appropriate for drawingapplications requiring relatively large amounts of power.

The die 12 has, for purposes of ease of attachment to acoustical coupler40, an axially extending portion 42 (see FIGURE 1A) to whose outersurface one end of coupler 40 is secured by means of cooperatingthreads. The other end of coupler 40 which is remote from the die,namely, each of the horn ends 44a, 44b, 44c, and 44d, is fixedly securedto a transducer. That is, horn end 44a is joined to transducer 50a, hornend 44b is joined to transducer 50b, 440 is joined to 50c, and 44a isjoined to 50d, preferably by brazing or some other type of metallurgicaljoint.

Acoustical coupler 40 is essentially a mechanical transformer and is ofcontoured construction for purposes including the increasing of theamplitude of vibration. Reference is made to United States patentapplication Serial No. 114,932 filed June 5, 1961, in the names of JamesByron Jones et al., entitled Three Limb Vibratory Device, which isco-pending, for details concerning construction of a coupler such ascoupler 40 and its associated plurality of transducers such astransducers 50.

The horn-type construction of system 38 is particularly suitable forapplication of relatively high levels of vibratory energy at a givenfrequency, and for avoiding undesirable modes of vibration in connectionwith both the powering and the operation of a relatively large singlecoupler, as well as for appropriate access and attachment to a membersuch as the die in order to vibrate it axially of the direction of draw.

Preferably, for support purposes and to minimize frequency shift of thevibratory apparatus and loss of vibratory energy to the associatedsupporting members, the die 12 is supported by a force-insensitive mount52.

Such force-insensitive mount 52 may comprise a sleeve, one-halfwavelength long at the operating frequency and made from steel or otherlow hysteresis material such as nickel, aluminum-bronze,beryllium-copper, or Monel. One end of the sleeve 52 is metallurgicallyjoined to the coupler 40, preferably at an antinode or loop region ofthe vibration on the cylindrical portions of the latter, and the otherend of the sleeve 52 is free from attachment. Sleeve 52 is provided witha radially outwardly extending flange 58 located one-quarter wavelengthfrom its attached end, and a true node will develop at flange 58.Reference is made to United States Patents Nos. 2,891,178; 2,891,179;and 2,891,180 each of which issued in the name of William C. Elmore andis entitled Support for. Vibratory Devices.

Flange 58 is removably secured to a support 60, as by a clamping ring 61and suitable bolts. Support 60 is rigidly secured to the draw bench 36.

The mount 52 in the drawing comprises a conical tubular member (a formwhich is not necessarily preferred). It will be appreciated that,instead of being formed and positioned as shown, mount 52 may comprise aplurality of more or less rodlike members, all having flanges and somebeing attached to each of the straight portions of horns 44a, 44b 44c,and 44d. This may be desirable, as, for example, in associating mount 52with coupler 40 in the section not representing an increase in amplitudeof vibration, thereby minimizing the subjection of mount 52 to theincreased stresses associated with the maximum amplitude implicit to thecontoured portion. If this latter configuration is used, the position ofthe support members relative to the draw bench will also be adjustedaccordingly.

Acoustical coupler 40 and die 12, like support mount 52, are preferablymade from K-Monel or other material having low hysteresis, goodelectrical and thermal conductivity, and high acoustical transmissionefficiency even when strained as much as 0.001-inch per inch, forexample, including such materials as nickel-aluminumbronze orberyllium-copper. The materials named are non-magnetic and are known tothe art for their relatively good acoustical power handling qualities.However, for drawing purposes the die 12 may be made of other materials,such as those chosen principally for suitability for the drawingoperation per se rather than for their acoustical properties, providedthat such change is material for the die is taken into consideration inconnection with design of the system for operation at a resonantfrequency, as has been indicated to be preferable for purposes of thepresent invention.

In accordance with the present invention, there is provided afree-floating plug 16 having a forming end 18 and a free-floating end20. Plug 16 may comprise a single member, or forming end 18 andfree-floating end 20 may be manufactured as separate members which maybe fixedly connected (as by a metallurgical joint such as a brazedjoint) or removably connected (as by cooperating threads). As shown inFIGURE 1A, a washer 28 of a soft material such as aluminum may bedisposed between the juxtaposed end faces of the forming end 18 and thefree-floating end 20, which washer 28 is compressed or deformed when theforming end 18 is threaded to the floating end 20 to assure a goodacoustic coupling if a screw connection is employed. Plug 16 (likecoupler 40, die 12, and mount 52) is preferably made from the abovementioned materials. However, as with die 12, the forming end 18 may bemade of a material (such as tungsten carbide, for example) chosenprincipally for suitability for the drawing operation per se, providedthat such material change is taken into consideration in connection withthe design of plug 16, as will be explained hereinbelow.

In operation, as shown in FIGURES 1 and 1A, the forming end 18 of plug16 extends into and through the orifice 14 and defines with the die 12 arestricted passageway through which the tube material 30 is drawn.

Plug 16 (like transducer-coupling system 38) is designed to operate at agiven frequency, which as aforesaid is preferably a resonant frequency,namely, the design frequency of system 38 (such as the 15,000 cycles persecond above mentioned, for example). Thus, plug 16 is preferablydimensioned to have a resonant length, namely, an over-all physicallength equivalent to an acoustical length of a single one-halfwavelength or a whole number multiple of one-half wavelength in thematerial of which it is made at the said frequency. This is so that itwill vibrate in the direction of the vibration of system 38, and so asto have for efficient operation an antinode or loop area of thevibration at the tubecontacting portion of the fonmin-g end 18 of theplug 16, namely, juxtaposed to the die orifice 14. Hereinafter, thetube-contacting portion of the forming end 18 at which is provided anantinode or loop area may be referred to as location 22. Preferably,plug 16 has a length of a whole even number multiple of one-halfwavelength so as to have each of its two ends 18 and 20 operating inphase.

Thus, as indicated in FIGURE 1A, assuming for simplicity of explanationthat the plug 16 is a single onehalf wavelength long, there will be anantinode of vibration at the locations designated generally as 22 and 24respectively and a node of vibration at the protrusion designatedgenerally as 26.

It is to be noted that the relatively minor protrusion in length offorming end 18 beyond the smallest diameter of the die orifice 14 andtherefore beyond the aboveindicated antinodal region 22 may involve aslight adjustmnt in the aforesaid acoustical length of plug 16, suchadjustment being well within the skill of one skilled in the art.

As is well known, the velocity of compressional waves in a medium variesaccording to the medium, and the appropriate length of plug 16 may befound by use of the well known equation (wavelengthzvelocity/frequency)showing the relation among frequency, velocity, and wavelength of sound.Thus, if the plug 16 is to be made of K-Monel, the velocity of sound inK-Monel is reportedly 4,480 meters per second, so that at a frequency of15,000 cycles per second a single one-half wavelength in K- Monel wouldbe 5.88 inches.

If all of plug 16 is to be made of K-Monel except for the forming end18, and if the forming end 18 is to be made of tungsten carbide as iscommon in the drawing art, the velocity of sound in the tungsten carbideused is ascertained (reportedly approximately 4200 meters per second,although various tungsten carbides may have various values for Youngsmodulus and density which will result in various velocities of sound),and the onehalf wavelength dimension is calculated (5.51 inches, usingthe above indicated 4200 meters per second and 15,000 cycles persecond). Then, dependent on the length needed for drawing reasons forthe tungsten carbide forming end 18 (with due consideration of itsconfiguration, such consideration being within the skill of the art),the K-Monel length and the tungsten carbide length of plug 16 can beadjusted so as to conform with the wavelength dimensioning requirementsabove indicated for plug 16.

The free-floating end 20 of plug 16 may have a straight outline form(such as being in the form of a rod) so as to be entirely free-floating,or it may have a rod-like form except for radially outwardly directedprotrusions at the nodal area (or one or more of the nodal areas, if theplug 16 has a length longer than a single one-half wavelength) such asare shown more clearly in FIGURE 1A. These protrusions serve to assistin the centering of the plug 16 with respect to both the tubing 30 andthe die orifice 14, and their location along plug 16 is such as tominimize the effect of their presence on the vibratory characteristicsand operation of plug 16. Allowance for such protrusions in connectionwith the wavelength dimensioning of plug 16 is entirely within the skillof the art. The outward extent of such protrusions or protrusion shouldbe sufiicient for aid in centering, but should not be so great as tocontact the interior of the wall of the tubing even under vibratory 6activation conditions, though this outer limit for the extent should beapproached as nearly as possible for centering reasons.

In operation, tubing 30 is telescoped over the plug 16 (usually aftertubing pro-treatment such as pickling, cleaning, and lubrication,although tubing pre-treatment may be minimized or eliminated in someinstances and with some materials when the present invention is used).The plug 16 is so arranged that the plug forming end 18 floats in theproper position in the die orifice 14. The tubing 30, in accordance withstandard practice, is pointed, i.e., provided with a reduced outsidediameter end portion such as end portion 32, which may be ac complishedin a variety of ways including swaging. Such reduced end portion 32 isfed in the direction of arrow through the die orifice 14. The jaws 64aand 64b of a pulling device 62 are clamped to the reduced end portion 32of the tubing 30. Pulling device 62 is movably mounted on drawbench 36for pulling the tubing 30 through the passageway defined by die 12 andforming end 18 of plug 16. The pulling device 62 is first actuated inthe direction of arrow 90 to seat the forming end 18. That is, thetubing 30 is pulled in the direction of arrow 90 until the tubing 30 islocked between the die orifice 14 and the outer peripheral surface ofthe forming end 18 of plug 16. As shown more clearly in FIGURE 1A, theforming end 18 of the plug 16 has an enlarged diameter portion which isgreater in transverse dimensions than the corresponding dimensions ofthe smallest diameter of the orifice 14 so that the plug 16 cannot bepulled through the orifice 14.

The tubing 30 can be translated by the pulling means for a shortdistance, so that the plug will seat properly and drawing can be readilyaccomplished. However, the invention is not limited to any particularsequence of steps in pointing the tubing and/or seating the plug,although certain sequences may be far more favorable. As is readilyevident, various lengths of tubing may be accommodated in accordancewith the present invention, including very long lengths as, for example,in continuous drawing.

After the forming end 18 of plug 16 is properly seated and positioned,and vibratory energy is applied to the system 38 including die 12 (andby reason of its acousti cal geometry to the plug 16), the pullingdevice 62 will move the jaws 64a and 64b in the direction of arrow 90. Awide variety of devices may, of course, be utilized to pull the jaws 64aand 6412, such as a hydraulic cylinder, a cable windup device, etc. Itwill be appreciated that the jaws 64a and 64b will be provided withmeans for selectively opening and closing the same, so that the reducedend portion of the tubing 30 may be inserted and gripped therebetween.

It will be appreciated that the power input to the transducers may bevaried according to the operating conditions utilized, including thematerial being drawn and the conditions of draw (such as the reductionto be achieved, the drawing speed, and the drawing tension), and alsoaccording to the transducer-coupling system and plug employed.

The position of the forming end 18 of plug 16 relative to the die 12 anddie orifice 14 is a determinant of the depth of draw, and afree-floating plug such as plug 16 is more susceptible to dislodgement(under conventional drawing conditions as well as under vibratoryactivation conditions) then is a back-supported plug, for example.

The amount of power supplied and transmitted to the die area should notbe sufficient to dislodge the forming end 18 of plug 16 from itslocation specified for drawing purposes. On the other hand, the powershould be suflicient to accomplish the given reduction under a given setof operating conditions for a given material.

As is well known to those skilled in the art, power output (to the work)of acoustical vibration devices is not readily ascertainable directly,and indirect determination thereof often involves the use of liquids andother aspects not suitable for ready adjustment to differing industrialapplications. Moreover, permissible power input is variable according tothe transducer utilized and the acoustical coupler geometries andmaterials used, as well as such factors as the efficiencies of jointsbetween the various members of the transducer-coupling system. Forexample, a magnetostrictive transducer is far more rugged andtrouble-free than the ceramic transducers which have been in commercialuse, but it has a lesser efiiciency in converting electrical power intomechanical vibration, and steel is a more readily machinable andjoinable coupler material than Monel or berylliumcopper, but it has alesser acoustical transmission efficiency. The implications are obviousfor differing amounts of acoustic power (expressed in electrical wattsoutput from the power supply or input to the transducer) used withvarious equipment, even without taking a given drawing operation intoconsideration.

For those desiring to insure continued transmission efiiciency for agiven system (in order to obtain warning of malfunction, for example),or for those desiring to compare the relative transmission efficienciesof a plurality of systems, means may be used such as are described inco-pending patent application Serial No. 66,642 filed November 1, 1960,for Method and Apparatus for Measurement of Acoustic Power Transmissionand Impedance by Dennison Bancroft et al.

For purposes of insuring a sufficient level of acoustical energy forpurposes of the present invention, it is to be noted that provision hasbeen made, in addition to a sufiicient level of electrical power inputto the transducer, for acoustical amplitude transformation. Also, thisacoustical amplitude transformation should preferably involve, when amagnetostrictive transducer is used, a total transformer ratio (from thedriving face of the transducer to the point of energy utilization) inthe range of from about 3.0 to about 7.5. When an electrostrictivetransducer (such as one of lead zirconate titanate) is used, suchtransformer ratio should preferably be in the range of from about 1.5 toabout 5. This ratio depends in part upon the material or materials ofwhich the coupling system member or members is made. The transformerratio is of particular importance for purposes of most efi'icient (andmost economical) utilization of the vibratory energy for drawing.

A lubricant may be applied to the inner and/or outer surfaces of thetubing 30 by means well known in the art. Such lubricants andlubrication are well known to the art and do not form a part of thepresent invention, except to the extent that the present invention (withsome materials and under some conditions of draw) enables elimination orminmization of lubircation, including a lessening of criticalityconcerning the use of a special lubricant for a given material.

A principal advantage of the present invention is the provision of afree-floating plug, such as is known to the drawing art, with vibratoryactivation such as is desirable for reasons indicated below, but Withoutthe necessity for making said plug a component element of atransducercoupling system. This is contrary to previous theory andpractice, in view of the plurality of interfaces involved which wouldordinarily be expected to cause considerable loss of acoustical energy.Also, plug 16 cannot be made a component element of atransducer-coupling system if practical continuous or long-tube drawingis to be employed; there are insurmountable access problems.

The preferred resonant length dimensioning of plug 16, above indicated,apparently causes said plug to vibrate in phase with the vibration ofthe die 12, thereby providing optimum material plasticity with resultantoptimum drawing tension reduction, decreased chattering tendencies,increased drawing speed, and greater material reductions per pass thanare obtainable in conventional free-floating plug drawing.

In view of the free-floating end 20 of plug 16 being acoustically freeat its outer end (i.e., delivering no vibratory energy in view of theacoustical impedance mismatch with air), the nodal regions at odd wholenumber multiples of one-quarter-wavelength from said end 20s outer endare true nodes, which is a condition non-achievable as a practicalmatter, so far as is known, in a transducer-coupling system under powerdelivery conditions.

As aforesaid, this invention is not limited to any particular sequenceof steps in pointing the tubing 30 and seating the forming end 18 ofplug 16, and the order of pointing and seating in the operation is notcritical to the present invention. For example, and as may beparticularly desirable in applications contemplating relatively higherarea reductions per pass for a given material, the system 38 may firstbe energized, the reduced cross section end of the tubing may bethreaded through the die orifice (with or without assistance of thepulling device, which device may aid in a desirable amount of sinking ofthe reduced cross section end of the tubing), and the forming end 18 ofplug 16 may then be advanced into the tubing 30 and seated as desired.Advance activation of the system 38 before seating may serve to simplifyproduction operations. It may also minimize likelihood of undesirabletubing metal pickup by the unenergized plug 16s forming end 18 duringseating, such as may be encountered With certain materials or withrelatively high area reductions for a given material.

For efficient operation, the pulling device 62 (including the jaws 64aand 64b) should be acoustically noncompliant. That is, the pullingdevice should not resonate in any mode at the frequency but should beessentially acoustically non-responsive, a condition attainable byvarious known means including appropriate adjustment of mass.

Although the invention is shown and described in connection with thedrawing of tubes, it is to be understood that the invention isapplicable generally to the drawing of elongated articles having wallstructure formed at least partly about a longitudinal axis thereof.

The present invention may be embodied in other specific forms withoutdeparting from the spirit or essential attributes thereof and,accordingly, reference should be made to the appended claims, ratherthan to the foregoing description as indicating the scope of theinvention.

I claim:

1. Vibratory tube drawing apparatus comprising a die having an orificetherein, a vibratory generator coupled to said die, means on one side ofsaid die for pulling tubing in an axial direction through said orifice,a free-floating plug partially disposed in said orifice, said plughaving a length equal to an integral number of one-half wavelengths inthe material of Which it is made at the frequency of said vibratorygenerator, said plug having one end thereof in said orifice and a secondend thereof on the side of said die opposite from said pulling means.

2. Apparatus in accordance with claim 1 wherein said plug has a lengthof a whole even number of multiple of one-half wavelength in thematerial of which it is made at the frequency of said vibratorygenerator whereby each of its ends operates in phase.

3. Apparatus in accordance with claim 1 wherein said plug includes anenlarged centering portion, said enlarged centering portion beinglocated at a node of vibration and having an outer diameter slightlyless than the inner diameter of a tube to be drawn.

4. The apparatus of claim 1 wherein said plug one end being manufacturedof a harder material than said second end, said second end and one endbeing acoustically coupled to one another.

5. The apparatus of claim 4 wherein said second end is rod-shaped, saidone end having a portion thereof of a greater diameter than saidrod-shaped second end, said second end having an expanded portion at anodal point therealong in the material of which the plug is made at thefrequency of said vibratory generator.

6. Apparatus for drawing elongated articles wherein said articles havewall structure formed at least partly about a longitudinal axis thereof,said apparatus comprising a die having an orifice therein, afree-floating plug extending at least paritally into said orifice fromone side of said die and defining with said die a restricted passagewayfor an article to be drawn, means associated with said die on the sidethereof opposite said plug for pulling an article through saidpassageway, a vibratory generator including a transducer and a couplercoupled to said die, said plug having a length equal to an integralmultiple of one-half wavelength in the material of which it is made atthe frequency of said vibratory generator, said transducer and couplerbeing arranged so as to vibrate in an axial direction so that avibratory loop occurs in said die.

7. A method of drawing tubes comprising the steps of providing afree-floating plug, telescoping a tube around the plug, feeding areduced diameter portion of said tube to a die, seating said plugagainst the portion of said tube juxtaposed to the orifice of said die,coupling vibratory energy to said die, inducing vibrations in said plugin phase with vibrations of said die, and pulling said reduced diameterportion of said tube in an axial direction away from said die to reducethe cross sectional area of said tube as it passes through said die.

8. The method of claim 7 wherein the step of providing a plug includesproviding a plug having a length equal to an integral number of one-halfwavelengths in the material of which is made at the frequency of thevibratory energy applied to said die.

9. The method of claim 7 wherein the step of pulling said reduceddiameter portion of said tube and the step of seating said plug againsta portion of said tube juxtaposed to an orifice of said die areaccomplished prior to said step of coupling vibratory energy to saiddie.

10. Vibratory tube drawing apparatus comprising a die having an orificetherein, a free-floating plug adapted to have one end extending at leastpartially into said orifice from one side of said die and defining withsaid orifice a restricted passageway for articles to be drawn, meansassociated with said die on the side thereof opposite from said plug forpulling an article through said passageway, a vibratory generatorcoupled to said die to vibrate said die in an axial direction withrespect to said orifice, said plug having a length equal to an integralmultiple of onehalf wavelength in the material of which it is made atthe frequency of said vibratory generator with a vibratory loop in theportion of said plug entering said orifice, an enlarged centeringportion on said plug located at a node of vibration and having an outerdiameter slightly less than the inner diameter of a tube to be drawn,and an enlarged diameter portion on said plug between said centeringportion and the smallest cross-sectional area of said orifice, saidenlarged diameter portion having a cross-sectional configuration whichis larger in transverse dimensions than the transverse dimensions of thesmallest crosssectional area of said orifice.

References Cited by the Examiner UNITED STATES PATENTS 2,525,258 10/50Fabrizio 2057 3,002,614 10/61 Jones 2072 FOREIGN PATENTS 1/57 Germany.

1. VIBRATORY TUBE DRAWING APPARATUS COMPRISING A DIE HAVING AN ORIFICETHEREIN, A VIBRATORY GENERATOR COUPLED TO SAID DIE, MEANS ON ONE SIDE OFSAID DIE FOR PULLING TUBING IN AN AXIAL DIRECTION THROUGH SAID ORIFICE,A FREE-FLOATING PLUG PARTIALLY DISPOSED IN SAID ORIFICE, SAID PLUGHAVING A LENGTH EQUAL TO AN INTEGRAL NUMBER OF ONE-HALF WAVELENGTHS INTHE MATERIAL OF WHICH IT IS MADE AT THE FREQUENCY OF SAID VIBRATORYGENERATOR, SAID PLUG HAVING ONE END THEREOF IN SAID ORIFICE AND A SECONDEND THEREOF ON THE SIDE OF SAID DIE OPPOSITE FROM SAID PULLING MEANS.